Subjective and objective rating of spectrally different pseudorandom noises—Implications for speech masking design

Abstract

Artificial sound masking is increasingly used in open-plan offices to improve speech privacy and to reduce distraction caused by speech sounds. Most of the masking sounds are based on pseudorandom continuous noise filtered to a specific spectrum that should be optimized in respect with speech masking efficiency and comfort. The aim of this study was to increase basic understanding regarding the comfort. The second aim was to determine how well objective rating methods (15 different noise indices) predict the subjective ratings. Twenty-three subjects rated the loudness, disturbance, pleasantness, and six other subjective measures of 11 spectrally different noises in laboratory conditions. Speech was not present during the experiment. All sounds were presented at 42 dB LAeq within 50-10,000 Hz. Unexpectedly, the subjects were most satisfied with sounds having emphasis on low frequencies. A sound having a slope of -7 dB per octave increment resulted in the highest satisfaction. Changes in subjective ratings were reasonably well predicted by five noise indices, while many well-known noise indices frequently used in building design underperformed in this task. The results are expected to benefit in the design of masking sounds and other appliances.

Perception of Water-Based Masking Sounds—Long-Term Experiment in an Open-Plan Office

“…This is in line with the laboratory experiment of Haapakangas et al (2011) which showed that the type of masking sound had an effect on cognitive performance and acoustic satisfaction even though the A-weighted SPL was constant. Additionally, Hongisto et al (2015) found that the spectrum alone explained the acoustic satisfaction of pseudo-random noises. Our study supports the findings of these previous studies but we cannot say which is more important: the spectrum or the type of sound.…”

“…Such a sound masking spectrum has been investigated in field conditions by, e.g., Helenius and Hongisto (2004), Hongisto (2008) and Hongisto et al (2012). A laboratory study of Hongisto et al (2015) showed that the subjects preferred a pseudo-random noise with a slope of −7 dB per octave doubling to a slope of −5 dB per octave doubling. Their study showed that the spectrum is an important basic feature of sound masking that should be carefully reported when the perception of sound masking is investigated.…”

Effect of self-adjustable masking noise on open-plan office worker’s concentration, task performance and attitudes

“…There are two potential reasons why these participants found the modified brown masking noise unpleasant. Firstly, the actual spectrum of the modified brown masking emitted by the earphones was distinctly different from brown masking noise used and found to be acceptable in previous studies (Hongisto, Oliva and Rekola 2015). On reflection masking noise such as those investigated by Haapakangas, Kankkunen, et al 2011 may have been more acceptable to the participants.…”

“…Noise with a spectrum of between -5dB per octave to -7dB per octave is considered to be close to brown noise (Hongisto, Oliva and Rekola, Subjective and objective rating of spectrally different psuedorandum noises -Implications for speech masking design 2015). A recent study has identified -7dB per octave as being an acceptable masking noise (Hongisto 2015). Of the eleven spectrally difference noises evaluated brown noise (-7dB per octave) resulted in the highest satisfaction.…”

Justification of standardized level differences in rating of airborne sound insulation between dwellings

“…Thereafter, the sound pressure levels L 2 in the receiving room could be calculated on the basis of level differences D. There are several noise ratings used in description of noise spectrum in a room [e.g. [25][26][27][28]. Our purpose was to find out how the SNQs for airborne sound insulation are associated with the levels of transmitted living sounds.…”